Method of producing gears



March 2 1945- f E. WILDHABER. 2,372,241

METHOD OF'PRODUCING GEARS I Filed May 24, 1941 5 Sheets-Sheet 1 lhwentor attorney March 27, 1945.

E. WILDHABER METHOD OF PRODUCING GEARS Filed ma 24, 1941 5 Sfieets -Sheet 2 lhwentqr ERNEST W/LDHHBEE 8g 5 z flung Mal ch 27, 1945. wlLDHABER 2,372,241

METHOD OF PRODUCING GEARS Filed May 24, 1941 5 Sheets-Sheet 3 ZSmaentor EFNES T WILD/1'1? BER attorney March 27, 1945. E. WILDHABER METIjOD 0F PRODUCING GEARS ,d May 24, 1941 5 Sheets-Sheet 4 3nventor fK/VES 7' W/LDHHBER March 27, 1945. E, WILDHABER 2,372,241

METHOD OF PRODUCING GEARS Filed May 24, 1941 5 Sheets-Sheet 5 m I 497711. Y ma i 1 l Aa my 14 F5. 15

'kNEs 7' WILD/{BEER Zhwentor (Ittorneg t- 'tooth profiles maybe finished but the tops of the Patented 27, 1945 METHOD OF PRODUCING GEARS Ernest Wildhaber, Brighton, N: Y assignor to Gleason Works, of New York r, N. Y., a corporation Application May 24, 1941 Serial No. 395,072

so Claims. (01. 90 -5) a The present invention relates to the cutting of gears and particularly to the cutting of longitudinally curved tooth evel and hypoid gears.

One object of the invention is to provide an improved method for cutting gears for transmitting non-uniform motionand'particularly gears of the varying-leverage type disclosed in my pending application, Serial No. 386,629, filed April 3, 1941, now Patent No. 2,308,558, issued January 19, 1943.

A further object of the invention is to provide a method for cutting gears with teeth of tapering depth for transmitting either uniform or nonuniform motion by which gears may be cut with a face-mill gear cutter that are mathematically correct and which will mesh without bias hearing.

A further object of the invention is to provide a method for generating non-uniform motion gears in which the same modification of generating roll may be employed in the generation of both sides of the gear teeth.-

Another object of the invention is to provide a method for cutting gears in which a gear may 7 be roughed out and one side finish-cut in a single operation and with a single cutter. 4

Still another object of the invention is to provide a method for cutting gears with which the gears may becompletely finish-cut from the solid in one operation and with a single cutter.

A further object of the invention is to provide '8 method for cutting gears which will permit of employing a cutter having a very large number of cutting blades soas to obtain either tooth suriiaees of finer finish or a higher speed of producon. i

. Another object of the invention is to provide a method for cutting gears in which not, only the teeth rounded in a single operationand with a single cutter. Y

.Still a further object of the invention is to provide a method for rough and finish cutting gears in a single operation and with a single tool in which the roughing is. effected by certain cutting edges of the tool whichdo'no finish-cutt ng,

and the finishing is effected by other cutting edges of the tool which do no rough-cutting but which are saved'for the finish-cutting only.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In cutting. gears according to the present invention, tools having cutting portions or points of zero pressure angle are used, and the tooth profiles of the gear are produced by imparting a cutting motion to the tool while effecting relative movement between the tool and the gear blank in such fashion that a tangent to the zero pressure angle cutting portion of the tool remains tangent to the tooth profile of the blank in all positions of contact between the tool and blank.

Varying-leverage gears, such as disclosed in my Patent No. 2,308,558, have tooth profiles which are concave for a portion of the height of a tooth and which are convex for the rest of the tooth height. These gears are capable of producing a greater variation in leverage during operation than any such gears heretofore proposed. To out such gears according to the process of the present invention a tool is used whose sidecutting edge has a convex portion that contains a point of zero pressure angle. The tooth profile is produced by impartinga cutting motion to thetool while effecting a relative rolling movement between the tool and gear blank and simultaneously producing a relative depthwise feed movement between the tool and blank in such timed relation to the rolling movement that the point of zero pressure angle in the cutting edge of the tool describes the desired concave-convex profile on the tooth. Both the ratio of rolling movement and the rate of feed are varied during cutting. Moreover, during the production of a given tooth surface; the feed movement is not continuous in one direction, but has two peaks.

The tool is first fed outwardly and then inwardly during generation of the described tooth profile. Part of the tooth profileis produced on the for-- ward roll and the remainder on the return roll.

For other forms of non-uniform motion gears, such as varying-leverage gears having wholly convex tooth profiles, cutting may be efiected during roll in one direction only. Here again, however, a tool of zero pressure angle is employed,

- and cuttingis effected by producing a relative roll between the tool and gear blank while efifecting a relative feed movement between tool and blank in time with the rolling movement.

For cutting gears that are intended to transmit uniform motion, the timed depthwise feed may be omitted. An involute toothprofile may be produced simply by rolling a toolotzero pressure angle and a gear blank relative to one another in such way that the point of contact between the 7 tool and'blank always remains in a plane tangent to thebase circle of the blank The tops ofthe teeth of such gears may be rounded off, if desired, however, by eiiecting a slight variation of the ratio or roll at the extreme ends or the roll.

The invention may be applied to the cutting 01 a tooth space in succession according to the pres both spur and tapered gears. In cutting tapered n in n ion:

gears, the teeth and tooth spaces are preferably Figs. 6 and 7 are a fragmentary side elevational a view and a fragmentary plan view, respectively. $55 11 55 1 53 1 2: g ii g gg further illustrating diagrammatically the method process of the present invention without "bias Show! F S- bearing." that is, without a tooth hearing or cona- 8 i a iasro m tw view. i l tr ms ne tact which xt nd diag nall of th t th, F possible form of drive that may be employed in uniform m ti gears, for instance, the'poims of a machine for practicing the present invention, to Contact between v tooth surface of matinggvw obtain a desired variation in thereto of roll; gears remain in the same plane a the lms 7 Figs. 3 and 10 are a. fragmentary SBCBlOIiB I and contact b twe th r l, wh m; either gear. a fragmentary plan View, respectively, or one and that gear during th generation f th t ge form of lace-mill gear cutter constructed for In the cutting of tapered gears, the depthwise icin the pres t i ve tion;

feed movement may e a gwmgmg e t Fig; 11 is a developed elevational view of one about the apex of the gearbeing out. Such a of the segments 01 this will; e motion has special advantage in the cutting of 1 i a fra mentary sectional view, dusnon uniform motion'tape efl gears, far n a trating the construction of the outside cutting swinging feed is used, the variation in ration! des a modified mm of face-mill gear roll required for generation of the. tooth profiles g9 cutter;

will b t same for opposite sides ft 13 l8 8. iragmentary sectional view, illusapplication of the present invention to the pro at 22 22g, 22:, 224, and 22s, res

V teeth of the gear shown mm. 3.;

Hence, the same controi' cam can be employed g ga i i f g l fi fii ig blade of during generation of one side oi the teeth of a is g to 17 i g arefiagmemary f igzj g of w 0151mm i Q as" tional views, illustrating the construction of other e e a 5 ggi 'ggg fi g g ef g gfggg gfi As already stated, Fig. 1 illustrates how a veryan g 5 9 an a s ace lug-leverage gear of concave-convex tooth prog 9 QZg 2 g and the g file-may be produced by the process of the presng part 0 a f m g out invention. A tooth of the gear is shown at size Sidfetlg tlile :1: may 6 g; r tgz 2a, and 2| designates the gear axis. The tooth s e e 3 space e i of has profiles 22 which are concave in their lower genera g r 1111 6 09905 s or flank portions and which are convex in their the tooth space may be i separate 35 upp'eror race portions. tool in a sepa t operation. In @0818 i i fi For cutting such gears, a tool 25 is used which however, it is P i l ush n W base-convex profile portion 2b. This tool may both sides of a t h liow 3 8 i i P be a reclprocatorir tool or. it may be a face-mill Here the tooth SW08 ma ke wt and 9? side gear cutter. In the case of a face-mill gear finish-out dun o p t of he he? h cu ter. corresponding side-cutting blades will have is set over relative to the work and the opposit convex profile portions such as shown at 26. The side of the tooth sp is s the convex portion 28 is so formed that there is a rest of the roll, Th cutting operation is e int 21 on this portion which is of zero pressure in such a way th the roughing of t e 5 angle or inclination. For a lace-mill gear cutter, tool does roughing On y and the fini 99 the tangent 28 to the profile 28 at the point 27 does no roughing but it is saved for finishing only, n be parallel to the cutter axm Since e- 1 cutting is done with only a To generate a tooth profile 22,'the tool and point of the-tool or with a m l P r 01 gear blank are made to perform such a motion pressure angle, t o need 1111 be 0 that the tangent 2a to the cutting edge reheisht. H nc it fflcermfll w cutter is used mains tangent to the tooth profile 22 being cut as the finishing tool, the cutter may have blades in all positions of contact between the cutting of relati e -S 3 fig gg edge 28 and the profile 22 with the result that great number of on g 8 68 may P 9 the point 21 graduall describes the rofile *2. in the cutter. Thus it is possible to obtain a very y p I In Fig. 1, a tooth profile 22 is shown in several fine Surface 13111511. nq h speed digerent positions of rotation about the gear or production. v v I axis 2| during generation of the tooth profile 22.

In the drawings: These positions are equally spaced angularly from Fig. 1 is a diagrammatic view, illustrating the ne another about the axis 2| and are denoted pectively. To production of varyin -leverage se having duce the'tooth profile 22, the tool is so moved cave-convex'tooth profiles; relative to the gear blank that when the various Fig.- 2 is a diagrammaticviemillustrating the points A, B, C, D, E, and F in the tooth profile app ica i n of'the pre en inve i o m are being cut, the tangents to the tooth profile ductlon or varying-leverage gears h ving wholly 22 at these points will also be tangent to the cutconvex tooth profiles: ting edge of the tool at the point 21, that is.

Fig. 3 is a dia rammatic view, illust a in e Will be parallel to the tangent 28. The tool thus method or successively roughing and flnish-c tdescribes relative to the gear a path such as ting one side of the teeth of uniform motion ,g in tt lines qe 'r path v gears according to the present lnventmm 5 7o Posed 01' a lateral component perpendicular to Fl:- 4 is a di 's a'mmafl e illustrating one the tangent a, which is the roll component, and

method of finish-cutting the opposite sides ot the an in-and-out depthwise feed movement in the .7 direction of the tangent 22. The rolling move- Fig. 5 is a diagrammatic view. illustrating a mom: must be performed with thesame high demethod or roughing and finishing both sides of 1| gree of accuracy as is commonly employed i the aevaaer generates, of gear teeth, but slight variation in the in-an'd-out feed movement is permissible since a slight error in position in the direction of the profile tangent 28 will have no measurable influence on the tooth profile shape produced.

To determine the path of generation required to produce a given tooth profile, normals are first drawn to the tooth profile at a series of points. Any such point is then turned about the gear center 2! through such an angle that in the final position the said normal extends in the direction of roll and the profile tangent is parallel to the tangent 28. In other words, a point in the tooth profile is turned through an angle equal to the inclination of its normal to the direction of roll. In this manner, the position of generation, and

- corresponding tool and work positions can readily be determined. Corresponding positions can, of course, be arrived at by computation based on the above procedure.

In Fig. 1, the various successive positions of the tool required for generation of the points A; B, C, D, E, and F of the. tooth profile are'denoted at 251, 252, 253, 254, 255, 256, respectively. As will be-seen from this figure, when a tooth profile such with a tool suitable for cutting the said side of the tooth. A gear of the type shown in Fig. 1 may first beroughed out in a forming or other suitable roughing operation and then finish-cut, one side at a time, by the method of the present invention.

It is possible, however, to rough out and finish one side in a single operation by the process of the present invention, and then to finish the other side. This methodv will be described later in further detail in connection with the description above the point 21. On a face-mill gear cutter,

. therefore, the gashesbetween successive cutting as shown at 22 is being generated, the dlsplacements of the tool during the generating r011 vary for equal angular movements of the work. Thus the lateral displacement between tool positions 251 and 252 is smaller than between tool positions 253 and 254. In other words, the ratio of movements of tool and work during generation-varies.

The depthwise feed movement also varies.

Moreover, it has two peaks whichv occur at the points of generation of the ends of the tooth profile 22. It is further to be noted that the tool is fed further in when the outer end or point of the-tooth profile is being generated at A than when the middle of the tooth profile is being provduced at the point E. Toproduce a convex-concave tooth profile such as shown at 22, the roll is reversed when the point E at the juncture of the convex and concave portions of the tooth profile has been cut, but the tool continues to feed further, in to cut the rest of the tooth profile. In this reversal of roll, the direction of the roll movement of the tool as well as the direction of "rotation of the work are reversed. The infeed movement continues, however, and is not reversed. It is only reversed after the lowest point in the tooth profile has been cut, which is a position, as

rotating in the reverse direction when cutting is taking place at the point F from the direction in which it is rotating when cutting is taking place at the point D. V I I The cycle illustrated in Fig. l is a finishing out. and for convenience in illustration it has been assumed that an infinitesimal finishing cut is be I .ing made in order to show how the profile is-described. Fig. 1 shows the generation 0! one side of atooth only. It will be understood, however, that the opposite side of the teeth may be generated by the same method as illustrated in Fig. 1'-

indicated clearly on the dotted line 30, that is blades can be made comparatively shallow with a bottom at 32, for instance. Hence, the height of the blades, viz., the distance between the lines 3| and 32, may be inade smaller than the height of the gear teeth to be cut. This makes it possible to provide the cutter with cutting blades that are closer together than in an ordinary facemill gear cutter. vided with more cutting teeth than an ordinary face-mill gear cutter so that a better tooth surface finish can be achieved, or more rapid production attained. I

Fig. 2 illustrates how the process of the present invention may be applied to the production of another type of varying-leverage gear where the tooth profile consists of a single convex circular are for most of its height with a sharply rounded convex portion at the top of the profile. Here the tooth profile can be fully described during rolling motion in one direction, and it is not necessary to cut on both the forward and return rolls in order to generate the complete tooth profile. 4U denotes a tooth of the gear whichis to be cut. ll is the axis of the gear, and 42 one ofthe tooth profiles. The tool 45- used for finish cutting the profile 42 has a straight side 46 of zero pressure angle and finishes the profile 42 with a point 41 of that profile. Here again, the generating motion comprises a lateral feed or roll in a directionperpendicular to the straight side 46 of the tool and an in-and-out depthwise feed motion in the direction of said side 46.

The tool may be a reciprocating tool or it may be aface-mil1 gear cutter whose axis is parallel to the side edge 46. In the latter case, the finishing surface of the tool comprises the cutting edges moves at a varyingvelocity relative to the work.

, of all the corresponding blades of the cuttergand is a cylindrical surface.

121, 42:, 42:, I24, and 42s denote successive positions of the tooth profile in the generating operation. These positions are spaced equiangularly from one another about the axis ll. In the production or the tooth profile, the tool Successive positions of the toolfor the shown angular positions of the tooth profile are denoted at 1, 452, 45:, 454. and 455, respectively. -The path of thepoint of contact between the tools and the tooth profile during generation is denoted at 40. When the tooth profile 42 has been completely described, the tool is withdrawn from engagement with the work, the roll is reversed to return the tool to initial position, the blank Hence, the cutter may be proment with the blank ready to describe another tooth profile of the blank. The dotted line 49 denotes the path of the tool during withdrawal;

the dotted line 50, the path of movement of the tool after it has, been withdrawn and while indexing is taking place; and the dotted line the path of movement of the tool while it is being fed back into engagement with the blank ready for the cutting of the next tooth profile.

In cutting cylindrical gears with a face-mill gear cutter that has an effective cutting portion of cylindical form, the individual depthwise positions of the tool are unimportant. Thus, it will be seen that the same tooth shape would be produced whether the tool is in the shown position 453 for the position d2: of the tooth profile or whether the tool is at some other position further in in the direction of tooth depth. This situation 'does not prevail, however, in the case of bevel gears where the in-and-out feed is a swinging feed about the apex of the gear. There the feed movement should be such as to insure that the tool attains the disclosed positions for the disclosed positions of the work, although even here some tolerance in the depthwise position of the tool for the different points of roll is permissible,

Use of the swinging feed about the gear apex in the generation of bevel gears according. to the present invention has the advantage that the motions employed are symmetrical for opposite sides of the teeth. The tooth profiles produced are also symmetrical, and the same roll modification can be used for all cone distances and cutter diameters.

Heretofore, it has been required to use facemill gear cutters of spherical form in order to produce varying-leverage bevel gears of tapered depth without bias. bearing? Mathematically correct varying-leverage level gears may be produced, however, by the method of the present invention and suchgears will mesh without bias bearing." Lengthwise localization of tooth bearing may be obtained, as usual, by providing facemill gear cutters for'cutting the two members of the pair which will cut longitudinally concave tooth surfaces on each member of the pair that have a radius of lengthwise curvature larger than the radius of lengthwise curvature of the mating longitudinally convex tooth surfaces of the other member of the pair.

Fig. 3 illustrates a method of cutting uniform motion bevel gears by the present invention with a face-mill gear cutter'and in such manner as to avoid bias bearing. This method may be employed for roughing the tooth slots and finishing one side from the solidin a single operation.

Here the pinion or gear to be cut is denoted at 60.

It has teeth 6i whose tooth profiles 62 and 63 are involutes having a base circle denoted at H. Tangent 65 to the base circle 64 is perpendicularto an involute tooth profile of the gear at the points of intersection of that profile with the tangent, as is well known. The tooth. profiles 63 of the gear may, therefore, be formed with a face-mill gear cutter '68 that has a straight finish-cutting portion 69 that is parallel to'the axis i l of the cutter and perpendicular to the tangent 55/ The-cutter is so positioned relative to the gear that a plane containing the tangent 6i and'pe 'pendieular tothe cutter axis 10 also contain the apex of the bevelgear. The tip surface '12 of the cutter extends inwardly at a constant distance below this 7 plane and cuts a' root surface II in a tooth, space of the gear which is parallel to the base cone 75 is indexed, and the tool is fed back into engageoi the gear. The root surface produced on the gear has, therefore, the same cone angle as the base cone but a difierent coneapex.

As in the previously described embodiments of the invention, the tooth profile 63 is finished by a single point is in the cutting edge 59 of the tool. The profile 63 is generated by rotating the blank'fiil on its axis at a uniform velocity while moving the tool 68 at a uniform velocity in the direction of the tangent $5. The finished tooth shape is generated bythe point M in the cutting edge of the tool as the point Hi travels along the tangent line 65. 681 denotes one extreme position of the tool during generation of the tooth profile $3, and 682 denotes another position in the generation of such profile. In the latter position, contact between the tool and the tooth profile takes place at the highest point in the tooth profile. The position of the tooth profile during generation of this point is denoted at 63'. The dotted line 35 denotes the path of travel of the point 14 of the cutting edge of the tool during withdrawal, while withdrawn, and during return and be fed either in the direction of its axis 170 or with a swinging feed about'the gear apex until it reaches full depth position 681. The depth iced may be made without generating roll, Then the roll begins and the involute profile 63 is described from the inside out during this generating roll. It will be seen that the finishing portion 69 of the tool does not cut during the infeed which is in the direction of said finishing portion. It is saved for finish-cutting. The depthwise cut is taken by the tip 12 of the tool and the cutting edges 1-6 and ill. The cutter is therefore a combination roughing and finishing cutter, having portions 69 used for finishing only, and other portions l6 and 11 used for roughing only. With this cutter and method it is good practice to rough and finish one side in one operation.

I tooth profile 62 is preferably generated from the outside inwardly. Initial positions of the cutter and 01' the tooth profile are denoted at Mr and 821, respectively. In'the generating operation,

' the work is rotated on it axisat a uniform velocity and a relative movement of translation is produced between the cutter and blank at a. uniform' velocity in' the direction of the tangent 84 to the base surface .64 oi the blank. In this movement, the point 86 inthe cutting edge 82 of the tool describes the toothproflle 62. line I! denotes the Path of movement of the e dotted then the generating roll is begun.

, ter is setover relative to'the gear blank, that is,

. with a single. tool according to another embodiment of the present invention. Here a gear so is to be out that has involute tooth profiles Q2 and 93.

Unlike the cutter of Fig. 4, the cutter 85 used.

in the method of Fig. 5 has both inside and outside cutting. edges. The inside and outside cutting edges may beprovided on each blade or on alternate blades. In the illustrated embodi ment, the cutter is shown as having opposite sidecutting edges which for a portion of their height are of zero pressure angle as denoted at 96 and 9'1. The remaining portions of the cutting edges are or positive pressure angle as denoted at M and 'lll2. r u For roughing and finishing a tooth space which has, opposite sides 92 and 93' of true involute' profile, the cutter is first'fed into depth and crating movement, the' work is' rotated on its axis at a uniform velocity and a'relatlve trans- 'latory movement is produced between the tool and blank also at a uniform velocity in the direction of, the tangent 98 to the base circle 99 of the blank. During this generating movement, the points 100 and IN. in opposite side cutting edges of the tool move along the tangent 98 and describe the involute tooth profiles 92 and 93.

On bevel gears, the rollalong tangent 98 is a turning motion on an axis 110 which is perpendicular to the plane containing said tangent and containing the gear apex H i (Figs. 6 and 7). The axis H passes through the apex Ill and the axis of the cutter is parallel'to the axis H0. The tip cutting edges I03 oi the cutter project below the base line 98 of the gear blankas a rule as shown in Fig. 5. They pro.-

ject the same amount beyond the apex ill, as shown in Fig.'6, so that the root cone H2 0! the blank has its apex at H3. H4 denotes the axisof the blank.

951, 952, 953, 954, and 955 denote diilerent posi- V producing a desired amount of profile mismatch In the gennotes a position of the tool where the set-over has been completed. The roll then continues to position 05:. During this part of the roll, the' point III in the side-cutting edge si-will complete the finished'tooth profile 93. The tool is then withdrawn from engagement with the blank and brought back to starting position and the blank is indexed.

When the opposite side-cutting edges are arranged on alternate blades, the finishing cuts may be taken by the points I00 and Illl under comparat'ively light cutting load. If desired, a Triplex type cutter may be employed having separate bottom-cutting and side-cutting blades so that the blades'which take the finishing cuts may be relieved of practically all except finish cutting.

Modification of the roll may be employed for between mating gears and, it desired, for round ing on the tooth-tops. This rounding oi! oi the tooth tops is illustrated in Fig. 5. It could be done very accurately with the straight finishingprofile 91' of the tool. This would lengthen the roll considerably, however. So the rounding oil is preferably produced, as shown, with the rounded point of the tool by varying the ratio of roll slightly at both ends of the roll. Thus, at the 1 beginning of the roll, the ratio of roll is so varied that the tool assumes the position 951 instead of the position shown in dotted lines at 95'. The latter position is the position which the tool would have were a true involut'e profile tions of the cutter during the generating operation. The roughing cut from the solid is taken at first by the top cutting edges I!!! of the cutter, but after the cutter has reached position 952, the roughing is also done by the inclined sideedges I02 and H34. It is never done, though, by the straightfinish cutting edges 96 and 91: Up to position 953, the roughing cuts are taken by the tip cutting edge I03 and side cutting edges I02 and IM while finishing is done by the point llll in the right hand side cutting edge 91.

- After one side 92 of the tooth space is finished, that is, after arriving at the position 95:. the cutit is automatically moved to a slightly different radial and angular. position. Thus, its axis may be moved from a position such as denoted at I05 in Fig. 7 to the position I05. -The'res'ult is that the tip J03 of the cutter will thereafter out along a path I08 instead of the path I". -It is as if the cutter had been slightly turned on an to be produced on the tooth surface for. the full height of the tooth surface. In theposition 951, the tool makes contact with the tooth profile 92 in the point I01, causing the rounding off of the profile 92 at its top. likewise, at the end of the roll, the ratio of roll is again slightly varied, causing the side-cutting edge 96 to make contact at thepoint II and round of! theprofile 93st it pwith themethod illustrated in Figs. 5, 6, and '1, it is possible to cut gears of zero or low spiral angle from the solid in a fast and accurate operation. The other methods described with relation to Figs. 3 and 4' are not confined to'gears of low spiral angle. They can be applied also to gears of high spiral angle provided that the base circle is notinside the root circle. Thiscondition is ordinarily present in mitre gearsand gears of low reduction; but may require special tooth design on gears of large reduction in orderto be achieved. The process of finishing from the solid as described with reference to Fig. 5 is also applicable to varying-leverage gear-shaving wholly convex tooth profiles, if the feed movement employed is a swinging movement about the cone apex. Even without the swinging feed, it can be used provided thata spherical cutter of low pressure angle is employed such as is-illustrated in Fig. 17. In this case, however, the motions. for the two sides are unsymmetrical. When the swinging feed is used, the motions for the two axis parallel to its own and passing through the small end of the tooth space being cutrwh'ile the' roll goes on. Inasmuch as the set-over is performed with the tool at full cutting depthand while cutting, the two set-over components should be timed with each other. This may be accomplished by hydraulic timing on known-types of spiral bevel gear generators. l'n Fig. 5, 954 desides are symmetrical so that computation of one side will do for both sides, and the same cams may be employed for all cone distances and cutdiameters for av given gear combination. The

ter cutter also is a simple tool.

Although for finishing lnvolute profiles, the work must be turned at a uniform rate for uniform roll movement of the cuttenconslderable time may be saved without sacrifice of accuracy by speeding up the roll when finishing sharply curved portions 01 the tooth profiles, Thus the portion of the cutting edge is for flnishingonly.

The outside cutting edges I" of the blades are of concave profile shape and are used for roughim; only. V Fig. illustrates a cutter of slightly difierent structure from that shown in Fig. 14. The cutter has again alternate inside and outside blades denoted at 191 and 192, respectively. The outside vention have been described, it will be understood that the invention is capable of further modification, and this application is intended to.eover any variaflons, uses, or adaptations of the invention, following, in general, the principles of V the invention and including such departures blade 192may be of the same structure as the blade 182, but the inside blade has an inside cutting edge I03 which is a circular are that conaxis of'the cutter, that is, which is of zero pressure angle.

In the cutters or both Figs. 14 and 15, the in side surfaces of the inside blades 181 and 19!,respectively, have a combined axial and radial outward, relief, being relieved in the directions of the arrows 181 and H51, respectively. The out: side surfaces of the outside blades 182 and 192, however, on account of their larger inclination or pressure angle may be relieved in an axial direction only as indicated by arrows 188 and 198, respectively.

' Fig. 16 shows a cutter suchas may be employed for practicing the invention according to the embodiment illustrated in Fig. 5. This cutter has inside cutting blades 201 and outside cutting blades 202. The inside cutting blade 201 has a finish cutting edge 203 which extends for part 01' the height of the blade and which is of straight profile and parallel to the cutter axis, that is,

' tains a point 15! whose tangent is parallel to the atapered gear blank so that its tip travels from one end of a tooth space to the other in a-direction inclined to the pitch surface of the blank to cut a tooth surface tapering in depth from end to end, while simultaneously efiecting a relative rolling movement between the tool and blank in -a plane which is perpendicular to the cutting edge of the tool at said point to generate the tooth profiles with said point.

2. The method of cutting tooth surfaces of a taperedgear which comprises positioning a facewhich is of zero pressure angle. It also has an inclined side-cutting edge 200 which is of positive pressure angle and is intended for rough cutting only. In a similar manner, the outside cutting blade 202 has a straight side cutting edge 20! 01' zero pressure angle for finish-cutting and an inclined cutting edge 205 of positive pressure angle for rough-cutting. The finish-cutting edges 203 and 205 are about as long or longer than the ac,- tive portions or the rough-cutting edges 204 and 208. The point width of the inclined cutting profiles 204 and 20$;when prolonged to the top 201 of the blade, is less than half the point width of the profiles 203 and 20S, and this point-width may, in fact, be zero or negative. The active sides of both the-inside and outside blades have combined radial and axial relief, being relieved in the directions of the arrows 209 and 210, respectively.

' Fig. 17 showsa. spherical cutter which has a mill gear cutter, whose side-cutting edges are of zero pressure angle at at least one point in their heights, in engagement with a tapered gear blank so that a plane tangent to the base. cone of the blank and perpendicular to the cutter axis also contains the pitch cone'apex of the blank, and rotating the cutter on its axis while producing a relative rolling movement-at a uniform velocity between cutter and blank so that points of contact between the said zero pressure angle portions of thecutter and the blanlr remain in very low pressure angle on both sides. It has inside cutting blades 211 and outside cutting blades 212. The inside cutting edge 213 of the inside cutting blade 211 is a circular are centered at 215 on the axis 216 of the cutter, while the outside cutting blade 212 has an outside edge 214 which is a circular are centered at!!! on the axis 216 of the cutter. The distance between the sphere centers 215 and 21! is less than one third of the mean radiusof the cutter, and the cutting edges of at least one side of the cutter contain 7 a point 219 of zero pressure angle. Sometimes the two centers 215 and 210 may coincide; Both the inside and the outside active surfaces of the cutter have combined radial and axial relief, being relieved'in the direction of the arrows 220 and 221, respectively. Cutters of this character may be used for cutting varying-leverage gearspf convex profile in one operation from the solid without in-an-out feed by a process which is analogous to the one described with reference to While several different embodiments of'the insaid tangent plane.

' 3. The method of cutting the tooth surfaces of I a gear which comprises moving a cutting tool,

'thathas a side-cutting edge of zero pressure angle at at least one point in its height, across the face of a gear blank while effecting a relative rolling movement at a varying ratio between the tool and blank and simultaneously producing a relative. depthwise feed movement at a varying velocitybetween the tool and blank in time with said rolling movement.

4. The method of cutting tooth surfaces of a gear which comprises moving a cutting tool, that has a side-cutting edge-of zero pressure angle at at least one point in its height, across the face of a gear blank while eflecting a relative rolling movement at a varying ratio between the tool and blank alternately in opposite directions to effect forward and return generating movements, r

and producing a relative depthwise feed movement during both the forward and return rolls until the tooth profile has been cut for its full height, then withdrawing the tool from engage ment with the blank, and indexing the blank.

5.The method of cutting tooth surfaces of a longitudinally curved tooth tapered gear which comprises positioning a face-mill gear cutter, whose blades have side-cutting edges of zero pressure angle at points below their tips, in engagement with a tapered gear blank so that the tip surface of the tool travels in a plane inclined to the pitch surface of the gear blank, and producing a relative rolling movement between the cutter and blank while effecting a relative angular feed movement between the cutter and blank about the apex of the blank until the tooth surface has been cut to full depth, then withdrawing the cutter irom. engagement with the blank, and

that the tipsof the blades travel from one end of a, tooth space to the other in a plane inclined to the pitch surface of the blank, and eifecting a relative rolling movement between the tool and blank in a plane perpendicular to the zero pressure angle portion of the blades in such timed portion of the cutting edge rough-cuts 'a side toothsuriace of the blank and the zero pressure angle portion finish-cuts the final profile shape of said tooth surface.

7. The method of cutting a gear which'cdmprises cutting its opposite side tooth surfaces withopposlte side-cutting edges, one of which is of straight profile and zero pressure angle for a part of its height and of positive pressure'angle .for the rest of its height and the other oil which is of positive pressure angle for its full height, and imparting a cutting motion to the tool while producing a relative rolling movement between the tool and blank in such timed relation that the positive pressure angle cutting edges rough out opposite sides-oi a tooth space of a blank and the zero pressure angle port h-cut one side of th space during'o generating cycle, and periodically indexing the blank.

8. The method of cutting a gear which comprises cutting its opposite side tooth surfaces T with a tool that has a tip cutting edge and opposite side-cutting edges, each of the side-cutting edges being of straight profile and zero pressure angle for a part of its height and of posirelation that a point in the cutting edge of the tool below the tip of the tool generates the final tooth profile shape.

11. The method of cutting tooth surfaces of a gear whiclrcomprises employing a face-mill gear cutter that has a plurality of annularly arranged cutting blades whose height is less than the height of the tooth surfaces to be cut and which have corresponding side-cutting edges that at points below the tips of the blades are of zero pressure angle, positioning said tool in engagement with a: gear blank so that the tip cutting edges of the tool travel from one end of a tooth space to the other in a plane inclined to the pitch surface of the blank, feeding the tool no the blank in the direction of the axis of the cutter, and producing a relative rolling movement between the cutter and blank in such timed relation with the iced motion that the finished tooth shape of the blank is generated by said points in the cutting edges or the tool below the tip of 1 the tool, then withdrawing the tool from engagetivepressure angle for'the rest of its height, by

imparting a cutting motion to the tool while producing a relative rolling movement between the tool and blank in such timed relation that the tip cutting edge of the tool and the positive pressure angle cutting edge at one side of the tool rough out one side of a tooth space of theblanli and the corresponding zero pressure angle out 1 ting edge finish-cuts that side of the tooth space during a part oi the generating cwcle, then shifting the tool relative to the blank and continuing "the generating cycle to cause the positive pressure angle and zero pressure angle cutting edges at the other side of the tool to rough and fiircut the opposite side of the tooth space, then withdrawing the tool from engagement with the blank and indexing the blank.

. 9. The method of cutting surfaces of a gear blank which comprises employing. a tool which has a cutting portion of zero piessure angle for part of its height and which is rounded at its tip, impa ing a cutting motion to the tool, while efiectinga relative rolling movement between the tool and blank to generate the tooth profiles; and varying the ratio of said rolling movement at one end, of the roll so that the rounded part of the tool will generate a round on the tip of the gear cloning the blank.

tooth, and periodically in- 10. The method of cutting tcoth surfaces of a 1 gear blank which comprises employing a face= mill gear cutter that has a plurality of circularly arranged cutting blades whose height is less than the height of the toothsuriaces to be cut and ment with the blank and indexing the blank.

12. The method of cutting tooth surfaces 0:? a gear which comprises employing a face-mill gear cutter that has a plurality of circularly arranged cutting blades which have convex side portions so curved that a tangent to a side portion of a blade at a given point therein is parallel to the axis oi the cutter, rotating the cutter in engagement with a gear blank while producing a relo= tive rolling movement at a varying ratio between cutter and blank and a relative depthwise feed movement at a varying rate between cutter and blank in such timed relation that the tangents to the cutting ed es of the cutter at'the specified points remain tangent to the tooth profile to he produced in all points of contact between the cutter and blank, and periodically indeidng the blank.

is. The method of cutting tooth surf es of a gear which comprises employing a face-mill gear cutter that has a plurality of circularly cutting blades which have ode-cutting edges ezmnd in the direction oi the axis or the cutter that been pluralityof circularly cuttingblades which have side-cutting edges that extend in a direction parallel to the axis oi e cutter, positioning smd cutter in engogement'wiifo which has corrcspon side-cutting edges that.

have a portion of zero pressure angle, positioning said tool in engagement with a gear blank so a gear. blank so that the cutterlwill cut tooth spaces in; the blank tapering in depth from to end, rotating the cutter in. engagement with the blank, enacting alternate movements of and withdrawal between the cutterv and blank about an axis passing, through the apex of the blank, and producing a relative rolling movement 7 between the cutter and blank in a plane penpendicular to said side-cutting edge; in such asvaau p v cutting movement to the tool while producing a timed relation with the feed movement that single points in corresponding cutting edges of the cutter constitute the points of contact betweenthe cutter and the tooth profile being generated,

- throughout the whole of the generation of that 16. The method of cutting the tooth surfaces 1 of a gear which comprises eifecting a relative rolling'movement between a cutting tool and the gear blank alternately in opposite directions at a varying ratio in such timed relation with a relative depthwise feed movement between the tooland blank that part of a tooth profile is generated during the forward generating movement and the remainder of the tooth profile is generated during the return generating movement. 1

' 17. The method of cutting the tooth surfaces of a gear which comprises effecting a relative 18. The method of cutting the tooth surfaces of a gear which comprises effecting a. relative rolling movement between a cutting tool and the gear blank alternating in opposite directions at a varying ratio in such timed relation with a relative depthwise feed movement at a varying rate between the tool and blank that part of a tooth profile is generated during the forward generating movement and the remainder of the tooth profile is generated during the return generating movement.

19. The method of cutting the tooth surfaces of a gear which comprises effecting a relative rolling movement at a varying ratio between a cutting tool and a gear blankalternately in opposite directions while producing a relative depthwise feed movement between the tool and blank'first outwardly and then inwardly at a varying rate, the inward feed movement occurring during the last part of the forward gener-' ating roll and during the first part of the return Y generating roll.

20. The method oi cutting tooth surfaces of a ear which comprises employing tool having a movement at a varying rate between the tool and blank in the direction of said cutting edge at said point. l

21. The method of cutting a tooth surface of a gear which comprises employing a tool having a side-cutting edge of zero pressure angle at at least one'pointinits heightaudimpartinga relative roiling movement at a varying ratio between the tool and blank in a direction perpendicular to the direction of said cutting edge at said point and simultaneously effecting a rela- 1 tive depthwise feed movement at a varying rate between the tool and blank in the direction of said cutting edge at said point.

'42. The method of cutting tooth surfaces of a gear blank which comprises efiecting a relative rolling movement at a, varying ratio between a cutting tool and the gear blankto generate a tooth profile and accelerating the. rate of the rolling movement at the end of the rolling movement to produce a round at the top of the tootn 23. The method of cutting the tooth surfaces of a gear which comprises effecting a relative rolling movement. at a varying ratio between a cutting tool and a gear blank while simultaneousLv effecting a relative depthwise feed move- .ment at a varying rate between the tool and blank to generate a tooth profile, and accelerating the rate of the rolling movement at the end of the rolling movement to produce a round at the top of the tootn profile. a j

2c. The method of cutting tooth surfaces of a gear which comprises moving a cutting tool, that has a side cutting edge of zero pressure angle at at least one point in its height, across the face or a gear blank while effecting a relative rolling movement at a varying ratio between the tool and blank, and producing a relative depthwise feed movement about the apex of the blank during the rolling movement until a side tooth surface of tne blank has been cut for its full height. then withdrawing the tool from engagement with the blank, and indexing the blank.

25. The method of cutting tooth surfaces of a "gear which comprises moving a cutting tool, that has a side cutting edge of zero pressure angle at at least one point in its height, across the face of a gear blank while effecting a relative rolling movement at a varyingratio' between the tool and blank alternately in opposite directions to effect forward and return generating move? ments, and producing a relative depthwise feed movement about the apex of the blank first outwardly and then inwardly during the rolling movement until a side tooth surface of the blank has been out for its full height, then withdrawing the tool from engagement with the blank, and indexing the blank.

26. The method of cutting side tooth surfaces of a tapered gear which comprises employing a face mill gear cutter, that has a cylindrical cutting surface whose axis coincides with the cutter axis, and rotating the cutter on its axis while effecting a relative rolling movement at a. varying ratio between the cutter and a gear blank, and

simultaneously producing a relative depthwise feed movement between the cutter and blank about the blank apex.

' 27. The method of cutting side tooth surfaces I of a gear which comprises effecting a relative rolling movement at a varying ratio between a cutting tool and a gear blank while producing a relative depthwise feed movement between the tool and blank first outwardly and then inwardly.

28.. The method of cutting side tooth surfaces of a tapered gear which comprises effecting a relative rolling movement at a varying ratio' producing a relative depthwise feedmovomsnt between a cutting tool and a gear blank whilebetween the tool and blank first outwardly and then inwardly about the blank apex.

29. The method of cutting side tooth surfaces of a tapered gear which'comprises employing a face mill gear cutter, that has side cutting edges which at at least one point in their height are of zero pressure angle, and rotating said cutter in engagement with a gear blank whileeifecting a relative rolling movement at a varying ratio between the cutter and blank, and simultane-' ously producing a relative depthwise feed movement between the cutter and blank first out-' wardly and then inwardly.

30. The method of cutting side tooth surfaces of a tapered gear which comprises employing a face mill gear cutter, that has side cutting edges which at at least one point in. their height are ofzero pressure angle, and rotating said outter in engagement with a gear, blank while efiecting a relative rolling movement at a varying ratio between the cutter and blank, and simultaneously producing a relative depthwise feed movement about the blank apex between the cutter and blank first outwardly. and then inwardly.

31. The method of cutting side tooth surfaces of a gear which comprises employing a cutting tool, that has a side cutting edge which has a finish cutting portion, that is of zero pressure angle adjacent its tip, and a rough cutting portion of positive pressure angle for the rest of its height, and imparting a cutting movement to the tool while effecting a relative rolling motion at a varying ratio between the tool and a gear blank in a plane perpendicular to the zero pressure angle portion of the tool.

32. The method of cutting side tooth surfaces aaraasr 34. The method of cutting side tooth surfaces of a gear which comprises employing a tool having a side-cutting edge of zero pressure angle at a point'below its tip, and'imparting a cutting motion to said tool while effecting a relative rolling movement at a vary ratio between the tool and the gear blank in a direction perpendicular to the said cutting edge at said point, while producing a relative depthwise feed movement between the tool and blank first outwardly and then inwardly in the direction of said cutting edge at said point.

'35. The method of cutting the tooth surfaces of a gear which comprises; employing a cutting tool, which has a side-cutting edge that is of zero pressure angle at a point below its tip, and imparting a cutting movement to the tool while producing a relative rolling movement between the tool and the blank alternately i opposite directions in a plane perpendicular to the cutting'edge of the tool at said point, and simultaneously eifecting a relative depthwise feed movement between the tool and blank'flrst outwardly and then inwardly at a varying ratio in the direction of the cutting edge of the tool at said point, the inward movement occurlng during the last part of the forward generating roll and during the first part of the return generating roll. 30

cave profile shape for part of their height and of a gear which comprises employing a cutting tool that has a side cutting edge which has a finish cutting portion, that is of zero pressure angle adjacent its tip, and a rough cutting por- 'tion of positive pressure angle for the rest of its height, and imparting a cutting movement to the tool while effecting a relative rolling movement at a varying ratio between the tool and gear blank, and simultaneously effecting a relative depthwise feed movement between the tool and blank about the blank apex.

33. The method of cutting a side tooth surface of a gear which comprises employing a tool having a rounded tip cutting edgeand imparting a cutting motion to the tool while effecting a relative rolling motionbetween the tool and the work, and varying the ratio of said rolling motion near the end of the roll to cause the tip cutting edge of the tool to round oil! the top or the gear tooth surface. 7

of convexproflle shape for the rest of their height, which comprises employing a face-mill gear cutter having circularly arranged cutting blades whose side-cutting edges are of zero pressure angle at points below their tips, and rotating said cutter in engagement with the blank while effecting a relative forward and return rolling motion between the cutter and blank in a direction perpendicular to the cutting edges of the tool at said points and at a varying ratio, and simultaneously producing a relative feed movement between the cutter and blank at a varying rate first outwardly and then inwardly in the direction of said cutting edges at said points, the forward part of the rolling movement being reversed when the said points in the cuttingedges are cutting at the juncture of the concave and convex portions of a tooth profile, and the inward part of the feed movement occurring during the last part of the forward roll andduring the first part of the return roll. 

